1. Field of the Invention
The present invention relates to a wireless communication, and more particularly, to a method of transmitting and receiving frames by stations operating in a power save mode in a WLAN system and an apparatus for supporting the same.
2. Related Art
In recent years, with development of information communication technology, various wireless communication technologies have been developed. Among them, a wireless local area network (WLAN) is technology that can wirelessly access the Internet in a home or an enterprise, or a specific service providing area by using a portable terminal a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), or the like based on radio frequency technology.
In order to overcome a limit in communication speed pointed out as a weak point in the WLAN, IEEE 802.11n is provided as a technological standard which has been established comparatively recently. IEEE 802.11n aims at increasing the speed and the reliability of the network and extending an operation distance of the wireless network. In more detail, IEEE 802.11n supports high throughput (HT) in which a data processing speed is maximum 540 Mbps or higher and is based on multiple inputs and multiple outputs (MIMO) technology using multiple antennas in both a transmitting unit and a receiving unit in order to minimize a transmission error and optimize a data speed.
In the wireless LAN system, the station (STA) supports a power save mode. The station operates by entering the doze state to prevent unnecessary power consumption. When there are traffics associated with data which are intended to be transmitted to the STA that operates in the doze state, the access point (AP) may indicate the traffics to the STA. The STA may recognize that the traffics associated with the data which are intended to be transmitted thereto exist and request transmitting the traffics to the AP. The AP may transmit a frame in response to the request from the STA.
Meanwhile, if the AP may transmit only one frame in response to the request by the STA that enters the awake state, it may be inefficient in terms of traffic processing. Further, since an operation of shifting the awake state/doze state is frequent in order for the STA to receive the buffered frame, efficiency may be decreased even in terms of a power save operation. Accordingly, a power save mode operating method is required, which is capable of achieving excellent traffic processing and improving power save mode efficiency of the STA.
Further, when a plurality of STAs associated with one AP is being operated in the power save mode and a relationship between the STAs is a relationship between hidden nodes, the STAs independently attempts a channel access in order to request transmitting buffered frames thereof, and as a result, a collision between requests by each STA may occur. Therefore, a frame transceiving method capable of solving the problem is required.